Collimator assembly for computed tomography system

ABSTRACT

A detector assembly  18  for an imaging system  20  is provided comprising a plurality of scintillator elements  50  positioned within a scintillator pack  56 . The scintillator pack  56  forms a scintillator pack upper surface  58  and a plurality of scintillator pack walls  60  positioned between the plurality of scintillator elements  50 . A plurality of collimator elements  64  are mounted on the scintillator pack upper surface  58 . Each of the plurality of collimator elements  50  is comprised of a stack laminated base  66  mounted to the scintillator pack upper surface  58  and a cast upper wall  68  formed on the stack laminated base  66.

BACKGROUND OF INVENTION

[0001] The present invention relates generally to a computed tomographyassembly, and, more particularly to a collimator and scintillatorassembly with improved manufacturing costs and accuracy.

[0002] Computed tomography has been utilized for a wide variety ofimaging applications. One such category of applications is comprised ofmedical imaging. Although it is known that computed tomography may takeon a wide variety of configurations within the medical industry, itcommonly is based on the transmission of low energy rays through a bodystructure. These low energy rays are subsequently received and processedto formulate an image, often three-dimensional, of the body structurethat can by analyzed by clinicians as a diagnostic aid.

[0003] The reception of the low energy rays, such as gamma-rays, isoften accomplished through the use of a device referred to as ascintillator camera. The scintillator camera is typically comprises of aplurality of structures working in concert to-receive and process theincoming energy rays after they have passed through the body structure.A collimator is an element often found in a scintillator camera that isused to limit the direction of photons as they approach the scintillatorelement. The collimator is commonly used to increase the magnificationof a viewed object or control resolution or field of view. Their primarypurpose, however, is to control the protons impinging on thescintillator element.

[0004] The scintillator element, in turn, is commonly a material withthe ability to absorb the protons and convert their energy into light.This allows the low energy rays received by the scintillator camera tobe converted into useful information. Scintillator elements may come ina wide variety of forms and may be adapted to receive a wide variety ofincoming rays. The light produced by the scintillator element iscommonly processed by way of a device such as a light sensitivephotodiode which converts the light from the scintillator element intoan amplified electronic signal. In this fashion, the information fromthe scintillator camera can be easily transferred, converted, andprocessed by electronic modules to facilitate viewing and manipulationby clinicians.

[0005] Current manufacturing methodologies for creation of scintillationcameras and the collimator components often present a multitude ofchallenges. The collimator components often consist of a matrix oftungsten plates in the z-direction and wires in the x-direction. Theseelements must be aligned with the scintillator and the x-ray focal spot.The height of the collimator elements in the y-direction is critical forscatter rejection. This scenario presents the following challenges:Plate bow along the z-direction is often realized. Alignment of the packto the collimator in both x and z-directions can be difficult. Focalalignment of the plates can be difficult and costly. Impropermanufacturing can result in undesirable sensitivity to focal spotmotion.

[0006] The plate/wire construction that presents the aforementionedchallenges has therefore prompted the development of new manufacturingtechnologies. Casting of collimator assemblies promises low cost andextensive cast heights. Casting, however, brings these benefits often atthe expense of dimensional accuracy from the top to bottom of thecasting. Stack laminations, alternatively, may also be utilized as itcan provide desired dimensional accuracy. Stack laminations, however,can result undesirable costs in addition to presenting limitations onstack height. Thus each approach can carry with it characteristics thatmay undermine its use in collimator manufacturing.

[0007] It would, however, be highly desirable to have a collimatorassembly that utilized the expense and sizing capabilities of castcollimators without suffering from the dimensional accuracy issues.Similarly, it would be highly desirable to have a collimator assemblythat utilized the dimensional accuracy of stack collimators withoutsuffering from the expense and height limitations associated with stackmanufacturing.

SUMMARY OF INVENTION

[0008] A detector assembly for an imaging system is provided comprisinga plurality of scintillator elements positioned within a scintillatorpack. The scintillator pack forms a scintillator pack upper surface anda plurality of scintillator pack walls positioned between the pluralityof scintillator elements. A plurality of collimator elements are mountedon the scintillator pack upper surface. Each of the plurality ofcollimator elements is comprised of a stack laminated base mounted tothe scintillator pack upper surface and a cast upper wall formed on thestack laminated base. Other features of the present invention willbecome apparent when viewed in light of the detailed description of thepreferred embodiment when taken in conjunction with the attacheddrawings and appended claims.

BRIEF DESCRIPTION OF DRAWINGS

[0009]FIG. 1 is an illustration of a computed tomography imaging systemfor use with the present invention.

[0010]FIG. 2 is a block schematic diagram of the computed tomographyimaging system illustrated in FIG. 1.

[0011]FIG. 3 is an illustration of a detector assembly in accordancewith the present invention.

DETAILED DESCRIPTION

[0012] Referring now to FIG. 1, which is an illustration of a computedtomography (CT) imaging system 10 for use with the detector assembly 18of the present invention. Although a particular CT imaging system 10 hasbeen illustrated, it should be understood that the detector assembly 18of the present invention can be utilized in a wide variety of imagingsystems. The CT imaging system 10 includes a scanner assembly 12illustrated as a gantry assembly. The scanner assembly 12 includes anx-ray source 14 for projecting a beam of x-rays 16 toward a detectorassembly 18 positioned opposite the x-ray source 14. The detectorassembly 18 includes a plurality of detector elements 20 which combineto sense the projected x-rays 16 that pass through an object, such as amedical patient 22. Each of the plurality of detector elements 20produces an electrical signal that represents the intensity of animpinging x-ray beam and hence the attenuation of the beam 16 as itpasses through the object of patient 22. Commonly, during a scan toacquire x-ray projection data, the scanner assembly 12 is rotated aboutthe center of rotation 24. In one embodiment, illustrated in FIG. 2,detector elements 20 are arranged in one row such that projection datacorresponding to a single image slice is acquired during a scan. Inother embodiments, the detector elements 20 can be arranged in aplurality of parallel rows, such that projection data corresponding to aplurality of parallel slices can be acquired simultaneously during ascan.

[0013] The rotation of the scanner assembly 12 and the operation of thex-ray source 14 are preferably governed by a control mechanism 26. Thecontrol mechanism 26 preferably includes an x-ray controller 29 thatprovides power and timing signals to the x-ray source 14 and a scannermotor controller 30 that controls the rotational speed and position ofthe scanner assembly 12. A data acquisition system (DAS) 32 in controlmechanism 26 samples analog data from the detector elements 20 andconverts the data to digital signals for subsequent processing. An imagereconstructor 34 receives sampled and digitized x-ray data from DAS 32and performs high speed image reconstruction. The reconstructed image isapplied as an input to a computer 36 which stores the image in a massstorage device 38.

[0014] The computer 36 also can receive commands and scanning parametersfrom an operator via console 40 that has a keyboard or similar inputdevice. An associated display 42 allows the operator to observe thereconstructed image and other data from the computer 36. The operatorsupplied commands and parameters are used by computer 36 to providecontrol signals and information to the DAS 32, x-ray controller 28, andscanner motor controller 30. In addition, the computer 36 operates atable motor controller 44 which controls a motorized table 46 toposition patient 22 within the scanner assembly 12. Particularly, thetable 46 moves portions of the patient 22 through the scanner opening48.

[0015] Each of the detector elements 20 of the detector assembly 18produces a separate electrical signal that is a measurement of the beamattenuation at the detector location. As illustrated in FIG. 3, thedetector assembly 18 includes a plurality of scintillator elements 50each of which is associated with one of the detector elements 20.Scintillator elements 50 are known devices that, when struck by x-rays,convert at least a portion of the energy of the x-rays into light thatcan be detected by the detector elements 20, commonly photodetectors 52.The photodetectors 52, such as photodiodes or photocells, are commonlyoptically coupled to the backs of the scintillator elements 50 and areutilized to generate electrical signals representative of the lightoutput from the scintillator elements 50. The attenuation measurementsfrom all detector elements 20 in the detector assembly 18 are acquiredseparately to produce a transmission profile. It should be understoodthat FIG. 3 illustrates a cross-section of the detector assembly 18 andis intended to be representative of both linear and multi-dimensionalarrays of detectors.

[0016] The scintillator elements 50 are preferably contained within ascintillator assembly 54 which comprises a scintillator pack 56.Although the scintillator pack 56 maybe constructed in a variety offashions, one embodiment contemplates the use of a cast scintillatorpack containing a reflector mixture. Although a variety of scintillatorpack 56 mixtures are contemplated, one embodiment contemplates the useof a castable material such as an epoxy, and a filler material. Thefiller material can include a reflective material sufficient toeffectively scatter and reflect light within the scintillator pack 56.The reflective material is cast or formed to generate a scintillatorpack upper surface 58 and a plurality of scintillator pack walls 60.Each of the scintillator pack walls 60 is positioned between two of theplurality of scintillator elements 50.

[0017] The present invention further includes a collimator assembly 62in communication with the scintillator pack 56. The collimator assembly62 is utilized to control the x-rays impacting the scintillator elements50. The collimator assembly 62 is comprised of a plurality of collimatorelements 64, each corresponding to one of the scintillator pack walls60. Prior collimator elements often provided either cost benefits ordimensional accuracy. The present collimator elements 64 provide aunique combination of these characteristics by including a stacklaminated base 66 and a cast upper wall 68. The stack laminated base 66is preferable bonded directly to the scintillator pack upper surface 56.The stack laminated base 66 assures accurate alignment with thescintillator pack walls 60. The increase accuracy allows the walloverlap 70 between the edge of the stack laminated base 66 and the edgeof the scintillator element 72 to be minimized. This improves coverageand thus increase output efficiency. In addition, the stack laminatedbase 66 allows for an accurate control of the collimator element 64height, as the lamination height dimension may be easily adjusted, whichallows for improved dimensional accuracy.

[0018] The collimator elements 64 combine the dimensional accuracyassociated by the stack laminated base 66 with the cost effectivecharacteristics associated with the cast upper wall 68. The cast upperwall 68 is preferably cast directly onto the stack laminated base 66with a cast wall thickness 74 less than the stack lamination width 76.In one embodiment, it is contemplated that the cast upper wall 68 may becast as a thin wall configuration having a substantially constant castwidth 74. In another embodiment, it is contemplated that the cast upperwall 68 may be cast with a tapered cast width 76 that decreased towardsthe cast upper edge 78. In addition, the tapered cast width 76 can beformed with an irregular surface 80 such that the taper is varied alongthe length of the cast upper wall 68. The combination of the stacklaminated base 66 and the cast upper wall 68 creates a collimatorassembly 62 that can be less sensitive to focal spot motion, can assureaccurate alignment relative to the scintillator elements 50, and canminimize the requirement for focal alignment while maintaining desiredscatter rejection properties.

[0019] While particular embodiments of the invention have been shown anddescribed, numerous variations and alternative embodiments will occur tothose skilled in the arm. Accordingly, it is intended that the inventionbe limited only in terms of the appended claims.

1. A detector assembly for an imaging system comprising: a plurality ofscintillator elements positioned within a scintillator pack, saidscintillator pack forming a scintillator pack upper surface and aplurality of scintillator pack walls positioned between said pluralityof scintillator elements; a plurality of collimator elements mounted onsaid scintillator pack upper surface, each of said plurality ofcollimator elements comprising; a stack laminated base mounted to saidscintillator pack upper surface; and a cast upper wall formed on saidstack laminated base.
 2. A detector assembly for an imaging system asdescribed in claim 1, wherein said stack laminated base includes a stacklamination width, said cast upper wall includes a cast wall thickness,and said cast wall thickness is less than said stack lamination width.3. A detector assembly for an imaging system as described in claim 1,wherein said cast upper wall can include a tapered cast width thatdecreases towards a cast upper edge.
 4. A detector assembly for animaging system as described in claim 3, wherein said cast upper wallincludes an irregular surface.
 5. A detector assembly for an imagingsystem as described in claim 1, wherein said cast upper wall comprises athin wall with a substantially constant cast width.
 6. A detectorassembly for an imaging system as described in claim 1, wherein saidcast upper wall is cast directly onto said stack laminated base.
 7. Adetector assembly for an imaging system as described in claim 1, whereinsaid stack lamination base includes a stack lamination width, said stacklamination base positioned to coincide with one of said scintillatorpack walls.
 8. A detector assembly for an imaging system as described inclaim 7, further comprising: a wall overlap defined between a side ofsaid stack laminated base and a side of one of said scintillatorelements, said stack lamination width minimizing said wall overlap.
 9. Adetector assembly for an imaging system as described in claim 1, whereinsaid scintillator pack comprises a cast reflector material.
 10. Adetector assembly for an imaging system as described in claim 1, furthercomprising: a plurality of detector elements, each on said plurality ofdetector elements in communication with one of said plurality ofscintillator elements.
 11. A detector assembly for an imaging system asdescribed in claim 1, wherein said stack laminated base is bondeddirectly to said scintillator pack upper surface.
 12. A detectorassembly for an imaging system comprising: a plurality of scintillatorelements positioned within a scintillator pack, said scintillator packforming a scintillator pack upper surface; a plurality of collimatorelements mounted on said scintillator pack upper surface, each of saidplurality of collimator elements comprising: a stack laminated basemounted to said scintillator pack upper surface, said stack laminatedbase including a stack lamination width; and a cast upper wall formed onsaid stack laminated base, said cast upper wall including a cast wallthickness, said cast wall thickness less than said stack laminationwidth.
 13. A detector assembly for an imaging system as described inclaim 12, wherein said cast upper wall can include a tapered cast widththat decreases towards a cast upper edge.
 14. A detector assembly for animaging system as described in claim 12, wherein said cast upper wallincludes an irregular surface.
 15. A detector assembly for an imagingsystem as described in claim 12, wherein said stack lamination baseincludes a stack lamination width, said stack lamination base positionedto coincide with one of a plurality of scintillator pack walls.
 16. Adetector assembly for an imaging system as described in claim 12,further comprising: a wall overlap defined between a side of said stacklaminated base and a side of one of said scintillator elements, saidstack lamination width minimizing said wall overlap.
 17. A detectorassembly for an imaging system as described in claim 12 wherein saidstack laminated base is bonded directly to said scintillator pack uppersurface.
 18. A method of generating a detector assembly for an imagingsystems comprising: stack laminating a collimator base onto ascintillator pack upper surface; casting a collimator upper wall ontosaid collimator base.
 19. A method of generating a detector assembly asdescribed in claim 18, further comprising: controlling the height of acollimator element by adjusting the height of said collimator base. 20.A method of generating a detector assembly as described in claim 18,further comprising: casting an irregular taper into said collimatorupper wall.
 21. A method of generating a detector assembly as describedin claim 18, further comprising: casting said collimator upper wall witha cast wall thickness less than a stack lamination width of saidcollimator base.